The present invention relates to a data transfer control device, electronic equipment, and a data transfer control method.
The universal serial bus (USB) standard 2.0 that supports high-speed (HS) mode is expanding well in the marketplace, but an interface standard called the USB On-The-Go (OTG) has been settled upon by the USB Implementers Forum (USB-IF). The OTG standard (OTG 1.0) that has been derived as an extension of USB 2.0 holds out the possibility of bringing out new additional value to the USB interface, and it is expected that applications that make use of these characteristics will appear.
This OTG makes it possible to impart a host function to a peripheral (peripheral device) connected to a host (such as a personal computer) by existing USB. This makes it possible to transfer data between peripherals connected by USB, enabling direct connection between a digital camera and a printer, by way of example, so that an image from the digital camera can be printed. It is also possible to connect a digital camera or digital video camera to a storage device, to save data therein.
However, it is usual for a peripheral that is given the host function by OTG to have a limited-capability CPU (processing section) incorporated therein. The addition of the host function therefore places a heavy processing load on the CPU (firmware) of the peripheral, making processing complicated and raising further problems such as impeding other processes and lengthening the design period of the device.
Giving a device the host function by OTG increases the size of the data transfer control device, which increases the cost of the data transfer control device, leading to further problems such as an increase in the cost of the electronic equipment in which the data transfer control device is incorporated.
Four different transfer methods are defined under USB, including a transfer method called control transfer. This control transfer is a transfer method that enables fetching of the information necessary for control of the peripheral, and this control transfer must always be supported by USB devices.
This control transfer is configured of a setup stage, a data stage, and a status stage, but if each of these stages is controlled and managed, a problem arises in that the processing load on the CPU (processing section, or firmware) becomes heavy.